Informational R. Pantos, Ed.
Internet-Draft W. May
Intended status: Informational Apple Inc.
Expires: April 18, 2013 October 15, 2012
HTTP Live Streamingdraft-pantos-http-live-streaming-10
Abstract
This document describes a protocol for transferring unbounded streams
of multimedia data. It specifies the data format of the files and
the actions to be taken by the server (sender) and the clients
(receivers) of the streams. It describes version 5 of this protocol.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. This document may not be modified,
and derivative works of it may not be created, and it may not be
published except as an Internet-Draft.
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This Internet-Draft will expire on April 18, 2013.
Copyright Notice
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document authors. All rights reserved.
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This Informational Internet Draft is submitted as an RFC Editor
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Internet-Draft HTTP Live Streaming October 20121. Introduction
This document describes a protocol for transferring unbounded streams
of multimedia data. The protocol supports the encryption of media
data and the provision of alternate versions (e.g. bitrates) of a
stream. Media data can be transferred soon after it is created,
allowing it to be played in near real-time. Data is usually carried
over HTTP [RFC2616].
External references that describe related standards such as HTTP are
listed in Section 11.
2. Summary
A multimedia presentation is specified by a URI [RFC3986] to a
Playlist file, which is an ordered list of media URIs and
informational tags. The URIs and their associated tags specify a
series of media segments.
To play the stream, the client first obtains the Playlist file and
then obtains and plays each media segment in the Playlist. It
reloads the Playlist file as described in this document to discover
additional segments.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. The Playlist file3.1. Introduction
Playlists MUST be Extended M3U Playlist files [M3U]. This document
extends the M3U file format further by defining additional tags.
An M3U Playlist is a text file that consists of individual lines.
Lines are terminated by either a single LF character or a CR
character followed by an LF character. Each line is a URI, blank, or
starts with the character '#'. Blank lines are ignored. White space
MUST NOT be present, except for elements in which it is explicitly
specified.
A URI line identifies a media segment or a variant Playlist file (see
Section 3.4.10). Each media segment is specified by a media URI and
the tags that apply to it.
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Lines that start with the character '#' are either comments or tags.
Tags begin with #EXT. All other lines that begin with '#' are
comments and SHOULD be ignored.
A URI in a Playlist, whether it is a URI line or part of a tag, MAY
be relative. Relative URIs MUST be resolved against the URI of the
Playlist file that contains it.
The duration of a Playlist file is the sum of the durations of the
media segments within it.
Playlist files whose names end in .m3u8 and/or have the HTTP Content-
Type "application/vnd.apple.mpegurl" are encoded in UTF-8 [RFC3629].
Files whose names end with .m3u and/or have the HTTP Content-Type
[RFC2616] "audio/mpegurl" are encoded in US-ASCII [US_ASCII].
Playlist files MUST have names that end in .m3u8 and/or have the
Content-Type "application/vnd.apple.mpegurl" (if transferred over
HTTP), or have names that end in .m3u and/or have the HTTP Content-
Type type "audio/mpegurl" (for compatibility).
3.2. Attribute Lists
Certain extended M3U tags have values which are Attribute Lists. An
Attribute List is a comma-separated list of attribute/value pairs
with no whitespace.
An attribute/value pair has the following syntax:
AttributeName=AttributeValue
An AttributeName is an unquoted string containing characters from the
set [A..Z] and '-'.
An AttributeValue is one of the following:
o decimal-integer: an unquoted string of characters from the set
[0..9] expressing an integer in base-10 arithmetic.
o hexadecimal-integer: an unquoted string of characters from the set
[0..9] and [A..F] that is prefixed with 0x or 0X and which
expresses an integer in base-16 arithmetic.
o decimal-floating-point: an unquoted string of characters from the
set [0..9] and '.' which expresses a floating-point number in
decimal positional notation.
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o quoted-string: a string of characters within a pair of double-
quotes ("), including Uniform Type Identifiers [UTI]. The set of
characters allowed in the string and any rules for escaping
special characters are specified by the Attribute definition, but
any double-quote (") character and any carriage-return or linefeed
will always be replaced by an escape sequence.
o enumerated-string: an unquoted character string from a set which
is explicitly defined by the Attribute. An enumerated-string will
never contain double-quotes ("), commas (,), or whitespace.
o decimal-resolution: two decimal-integers separated by the "x"
character. The first integer is a horizontal pixel dimension
(width); the second is a vertical pixel dimension (height).
The type of the AttributeValue for a given AttributeName is specified
by the Attribute definition.
A given AttributeName MUST NOT appear more than once in a given
Attribute List.
An Attribute/value pair with an unrecognized AttributeName MUST be
ignored by the client.
Any tag containing an attribute/value pair of type enumerated-string
whose AttributeName is recognized but whose AttributeValue is not
recognized MUST be ignored by the client.
3.3. Standard Tags3.3.1. EXTM3U
An Extended M3U file is distinguished from a basic M3U file by its
first line, which MUST be the tag #EXTM3U.
3.3.2. EXTINF
The EXTINF tag specifies the duration of a media segment. It applies
only to the media segment that follows it. Each media segment MUST
be preceded by an EXTINF tag. Its format is:
#EXTINF:<duration>,<title>
"duration" is an integer or floating-point number in decimal
positional notation that specifies the duration of the media segment
in seconds. Durations that are reported as integers SHOULD be
rounded to the nearest integer. Durations MUST be integers if the
protocol version of the Playlist file is less than 3. The remainder
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of the line following the comma is an optional human-readable
informative title of the media segment.
3.4. New Tags
This document defines the following new tags: EXT-X-BYTERANGE, EXT-X-
TARGETDURATION, EXT-X-MEDIA-SEQUENCE, EXT-X-KEY, EXT-X-PROGRAM-DATE-
TIME, EXT-X-ALLOW-CACHE, EXT-X-PLAYLIST-TYPE, EXT-X-STREAM-INF, EXT-
X-I-FRAME-STREAM-INF, EXT-X-I-FRAMES-ONLY, EXT-X-MEDIA, EXT-X-
ENDLIST, EXT-X-DISCONTINUITY, and EXT-X-VERSION.
3.4.1. EXT-X-BYTERANGE
The EXT-X-BYTERANGE tag indicates that a media segment is a sub-range
of the resource identified by its media URI. It applies only to the
next media URI that follows it in the Playlist. Its format is:
#EXT-X-BYTERANGE:<n>[@o]
where n is a decimal-integer indicating the length of the sub-range
in bytes. If present, o is a decimal-integer indicating the start of
the sub-range, as a byte offset from the beginning of the resource.
If o is not present, the sub-range begins at the next byte following
the sub-range of the previous media segment.
If o is not present, a previous media segment MUST appear in the
Playlist file and MUST be a sub-range of the same media resource.
A media URI with no EXT-X-BYTERANGE tag applied to it specifies a
media segment that consists of the entire resource.
The EXT-X-BYTERANGE tag appeared in version 4 of the protocol.
3.4.2. EXT-X-TARGETDURATION
The EXT-X-TARGETDURATION tag specifies the maximum media segment
duration. The EXTINF duration of each media segment in the Playlist
file MUST be less than or equal to the target duration. This tag
MUST appear once in the Playlist file. It applies to the entire
Playlist file. Its format is:
#EXT-X-TARGETDURATION:<s>
where s is an integer indicating the target duration in seconds.
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Internet-Draft HTTP Live Streaming October 20123.4.3. EXT-X-MEDIA-SEQUENCE
Each media segment in a Playlist has a unique integer sequence
number. The sequence number of a segment is equal to the sequence
number of the segment that preceded it plus one. The EXT-X-MEDIA-
SEQUENCE tag indicates the sequence number of the first segment that
appears in a Playlist file. Its format is:
#EXT-X-MEDIA-SEQUENCE:<number>
A Playlist file MUST NOT contain more than one EXT-X-MEDIA-SEQUENCE
tag. If the Playlist file does not contain an EXT-X-MEDIA-SEQUENCE
tag then the sequence number of the first segment in the playlist
SHALL be considered to be 0. A client MUST NOT assume that segments
with the same sequence number in different variants or renditions
contain matching content.
A media URI is not required to contain its sequence number.
See Section 6.3.2 and Section 6.3.5 for information on handling the
EXT-X-MEDIA-SEQUENCE tag.
3.4.4. EXT-X-KEY
Media segments MAY be encrypted. The EXT-X-KEY tag specifies how to
decrypt them. It applies to every media segment that appears between
it and the next EXT-X-KEY tag in the Playlist file with the same
KEYFORMAT attribute (or the end of the Playlist file). Two or more
EXT-X-KEY tags with different KEYFORMAT attributes MAY apply to the
same media segment, in which case they MUST resolve to the same key.
Its format is:
#EXT-X-KEY:<attribute-list>
The following attributes are defined:
METHOD
The value is an enumerated-string that specifies the encryption
method. This attribute is mandatory.
The methods defined are: NONE, AES-128, and SAMPLE-AES.
An encryption method of NONE means that media segments are not
encrypted. If the encryption method is NONE, the following
attributes MUST NOT be present: URI; IV; KEYFORMAT;
KEYFORMATVERSIONS.
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An encryption method of AES-128 means that media segments are
completely encrypted using the Advanced Encryption Standard [AES_128]
with a 128-bit key and PKCS7 padding [RFC5652]. If the encryption
method is AES-128, the URI attribute MUST be present. The IV
attribute MAY be present; see Section 5.2.
An encryption method of SAMPLE-AES means that the media segments
contain elementary streams of audio, video, or other samples that are
encrypted using the Advanced Encryption Standard [AES_128]. How an
elementary stream is encrypted depends on the media encoding. The
encryption format for H.264 [H_264], AAC [ISO_14496] and AC-3 [AC_3]
elementary streams is described by [SampleEnc]. The IV attribute MAY
be present; see Section 5.2.
URI
The value is a quoted-string containing a URI [RFC3986] that
specifies how to obtain the key. This attribute is mandatory unless
the METHOD is NONE.
IV
The value is a hexadecimal-integer that specifies the Initialization
Vector to be used with the key. The IV attribute appeared in
protocol version 2.
KEYFORMAT
The value is a quoted-string that specifies how the key is
represented in the resource identified by the URI; see Section 5 for
more detail. This attribute is optional; its absence indicates, an
implicit value of "identity". The KEYFORMAT attribute appeared in
protocol version 5.
KEYFORMATVERSIONS
The value is a quoted-string containing one or more positive integers
separated by the "/" character (for example, "1/3"). If more than
one version of a particular KEYFORMAT is defined, this attribute can
be used to indicate which version(s) this instance complies with.
This attribute is optional; if it is not present, its value is
considered to be "1". The KEYFORMATVERSIONS attribute appeared in
protocol version 5.
If the Playlist file does not contain an EXT-X-KEY tag then media
segments are not encrypted.
See Section 5 for the format of the key file, and Section 5.2,
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segment encryption.
3.4.5. EXT-X-PROGRAM-DATE-TIME
The EXT-X-PROGRAM-DATE-TIME tag associates the first sample of a
media segment with an absolute date and/or time. It applies only to
the next media segment.
The date/time representation is ISO/IEC 8601:2004 [ISO_8601] and
SHOULD indicate a time zone:
#EXT-X-PROGRAM-DATE-TIME:<YYYY-MM-DDThh:mm:ssZ>
For example:
#EXT-X-PROGRAM-DATE-TIME:2010-02-19T14:54:23.031+08:00
See Section 6.2.1 and Section 6.3.3 for more information on the EXT-
X-PROGRAM-DATE-TIME tag.
3.4.6. EXT-X-ALLOW-CACHE
The EXT-X-ALLOW-CACHE tag indicates whether the client MAY or MUST
NOT cache downloaded media segments for later replay. It MAY occur
anywhere in the Playlist file; it MUST NOT occur more than once. The
EXT-X-ALLOW-CACHE tag applies to all segments in the playlist. Its
format is:
#EXT-X-ALLOW-CACHE:<YES|NO>
See Section 6.3.3 for more information on the EXT-X-ALLOW-CACHE tag.
3.4.7. EXT-X-PLAYLIST-TYPE
The EXT-X-PLAYLIST-TYPE tag provides mutability information about the
Playlist file. It applies to the entire Playlist file. It is
optional. Its format is:
#EXT-X-PLAYLIST-TYPE:<EVENT|VOD>
Section 6.2.1 defines the implications of the EXT-X-PLAYLIST-TYPE
tag.
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Internet-Draft HTTP Live Streaming October 20123.4.8. EXT-X-ENDLIST
The EXT-X-ENDLIST tag indicates that no more media segments will be
added to the Playlist file. It MAY occur anywhere in the Playlist
file; it MUST NOT occur more than once. Its format is:
#EXT-X-ENDLIST
3.4.9. EXT-X-MEDIA
The EXT-X-MEDIA tag is used to relate Playlists that contain
alternative renditions of the same content. For example, three EXT-
X-MEDIA tags can be used to identify audio-only Playlists that
contain English, French and Spanish renditions of the same
presentation. Or two EXT-X-MEDIA tags can be used to identify video-
only Playlists that show two different camera angles.
The EXT-X-MEDIA tag stands alone, in that it does not apply to a
particular URI in the Playlist. Its format is:
#EXT-X-MEDIA:<attribute-list>
The following attributes are defined:
URI
The value is a quoted-string containing a URI that identifies the
Playlist file. This attribute is optional; see Section 3.4.10.1.
TYPE
The value is enumerated-string; valid strings are AUDIO, VIDEO and
SUBTITLES. If the value is AUDIO, the Playlist described by the tag
MUST contain audio media. If the value is VIDEO, the Playlist MUST
contain video media. If the value is SUBTITLES, the Playlist MUST
contain subtitle media.
GROUP-ID
The value is a quoted-string identifying a mutually-exclusive group
of renditions. The presence of this attribute signals membership in
the group. See Section 3.4.9.1.
LANGUAGE
The value is a quoted-string containing an RFC 5646 [RFC5646]
language tag that identifies the primary language used in the
rendition. This attribute is optional.
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NAME
The value is a quoted-string containing a human-readable description
of the rendition. If the LANGUAGE attribute is present then this
description SHOULD be in that language.
DEFAULT
The value is an enumerated-string; valid strings are YES and NO. If
the value is YES, then the client SHOULD play this rendition of the
content in the absence of information from the user indicating a
different choice. This attribute is optional. Its absence indicates
an implicit value of NO.
AUTOSELECT
The value is an enumerated-string; valid strings are YES and NO.
This attribute is optional. Its absence indicates an implicit value
of NO. If the value is YES, then the client MAY choose to play this
rendition in the absence of explicit user preference because it
matches the current playback environment, such as chosen system
language.
FORCED
The value is an enumerated-string; valid strings are YES and NO.
This attribute is optional. Its absence indicates an implicit value
of NO. The FORCED attribute MUST NOT be present unless the TYPE is
SUBTITLES.
A value of YES indicates that the rendition contains content which is
considered essential to play. When selecting a FORCED rendition, a
client should choose the one that best matches the current playback
environment (e.g. language).
A value of NO indicates that the rendition contains content which is
intended to be played in response to explicit user request.
CHARACTERISTICS
The value is a quoted-string containing one or more Uniform Type
Identifiers [UTI] separated by comma (,) characters. This attribute
is optional. Each UTI indicates an individual characteristic of the
rendition.
A SUBTITLES rendition MAY include the following characteristics:
"public.accessibility.transcribes-spoken-dialog";
"public.accessibility.describes-music-and-sound"; "public.easy-to-
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read" (which indicates that the subtitles have been edited for ease
of reading).
An AUDIO rendition MAY include the following characteristics:
"public.accessibility.describes-video".
The CHARACTERISTICS attribute MAY include private UTIs.
The EXT-X-MEDIA tag appeared in version 4 of the protocol.
3.4.9.1. Rendition Groups
A set of EXT-X-MEDIA tags with the same GROUP-ID value forms a group
of renditions. Each member of the group MUST represent an
alternative rendition of the same content.
All EXT-X-MEDIA tags in a Playlist MUST meet the following
constraints:
o All EXT-X-MEDIA tags in the same group MUST have the same TYPE
attribute.
o All EXT-X-MEDIA tags in the same group MUST have different NAME
attributes.
o A group MUST NOT have more than one member with a DEFAULT
attribute of YES.
o All members of a group whose AUTOSELECT attribute has a value of
YES MUST have LANGUAGE [RFC5646] attributes with unique values.
o All members of a group with TYPE=AUDIO MUST use the same audio
sample format.
o All members of a group with TYPE=VIDEO MUST use the same video
sample format.
A Playlist MAY contain multiple groups of the same TYPE in order to
provide multiple encodings of each rendition. If it does so, each
group of the same TYPE SHOULD contain corresponding members with the
same NAME attribute, LANGUAGE attribute, and rendition.
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Internet-Draft HTTP Live Streaming October 20123.4.10. EXT-X-STREAM-INF
The EXT-X-STREAM-INF tag identifies a media URI as a Playlist file
containing a multimedia presentation and provides information about
that presentation. It applies only to the URI that follows it. Its
format is:
#EXT-X-STREAM-INF:<attribute-list>
<URI>
The following attributes are defined:
BANDWIDTH
The value is a decimal-integer of bits per second. It MUST be an
upper bound of the overall bitrate of each media segment (calculated
to include container overhead) that appears or will appear in the
Playlist.
Every EXT-X-STREAM-INF tag MUST include the BANDWIDTH attribute.
PROGRAM-ID
The value is a decimal-integer that uniquely identifies a particular
presentation within the scope of the Playlist file.
A Playlist file MAY contain multiple EXT-X-STREAM-INF tags with the
same PROGRAM-ID to identify different encodings of the same
presentation. These variant playlists MAY contain additional EXT-X-
STREAM-INF tags.
CODECS
The value is a quoted-string containing a comma-separated list of
formats, where each format specifies a media sample type that is
present in a media segment in the Playlist file. Valid format
identifiers are those in the ISO File Format Name Space defined by
RFC 6381 [RFC6381].
Every EXT-X-STREAM-INF tag SHOULD include a CODECS attribute.
RESOLUTION
The value is a decimal-resolution describing the approximate encoded
horizontal and vertical resolution of video within the presentation.
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AUDIO
The value is a quoted-string. It MUST match the value of the
GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the Playlist
whose TYPE attribute is AUDIO. It indicates the set of audio
renditions that MAY be used when playing the presentation. See
Section 3.4.10.1.
VIDEO
The value is a quoted-string. It MUST match the value of the
GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the Playlist
whose TYPE attribute is VIDEO. It indicates the set of video
renditions that MAY be used when playing the presentation. See
Section 3.4.10.1.
SUBTITLES
The value is a quoted-string. It MUST match the value of the
GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the Playlist
whose TYPE attribute is SUBTITLES. It indicates the set of subtitle
renditions that MAY be used when playing the presentation. See
Section 3.4.10.1.
3.4.10.1. Alternative Renditions
When an EXT-X-STREAM-INF tag contains an AUDIO, VIDEO, or SUBTITLE
attribute, it indicates that alternative renditions of the content
are available for playback of that variant.
When defining alternative renditions, the following constraints MUST
be met:
o All playable combinations of renditions associated with an EXT-X-
STREAM-INF tag MUST have an aggregate bandwidth less than or equal
to the BANDWIDTH attribute of the EXT-X-STREAM-INF tag.
o If an EXT-X-STREAM-INF tag contains a RESOLUTION attribute and a
VIDEO attribute, then every alternative video rendition MUST match
the value of the RESOLUTION attribute.
o Every alternative rendition associated with an EXT-X-STREAM-INF
tag MUST meet the constraints for a variant stream described in
Section 6.2.4.
The URI attribute of an EXT-X-MEDIA tag is optional. If it is
missing, it indicates that the rendition described by the EXT-X-MEDIA
tag is present in the main Playlist described by the EXT-X-STREAM-INF
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tag.
Note that if a client chooses to play renditions of audio and video
that are not present in the main Playlist described by the EXT-X-
STREAM-INF tag, or if the client chooses to play an audio rendition
and the main Playlist is audio-only, then the client MAY ignore the
main Playlist and its media.
3.4.11. EXT-X-DISCONTINUITY
The EXT-X-DISCONTINUITY tag indicates an encoding discontinuity
between the media segment that follows it and the one that preceded
it. The set of characteristics that MAY change is:
o file format
o number and type of tracks
o encoding parameters
o encoding sequence
o timestamp sequence
Its format is:
#EXT-X-DISCONTINUITY
See Section 4, Section 6.2.1, and Section 6.3.3 for more information
about the EXT-X-DISCONTINUITY tag.
3.4.12. EXT-X-I-FRAMES-ONLY
The EXT-X-I-FRAMES-ONLY tag indicates that each media segment in the
Playlist describes a single I-frame. I-frames (or Intra frames) are
encoded video frames whose encoding does not depend on any other
frame.
The EXT-X-I-FRAMES-ONLY tag applies to the entire Playlist. Its
format is:
#EXT-X-I-FRAMES-ONLY
In a Playlist with the EXT-X-I-FRAMES-ONLY tag, the media segment
duration (EXTINF tag value) is the time between the presentation time
of the I-frame in the media segment and the presentation time of the
next I-frame in the Playlist, or the end of the presentation if it is
the last I-frame in the Playlist.
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Media resources containing I-frame segments MUST begin with either a
Transport Stream PAT/PMT or be accompanied by an EXT-X-MAP tag
indicating the proper PAT/PMT. The byte range of an I-frame segment
with an EXT-X-BYTERANGE tag applied to it (Section 3.4.1) MUST NOT
include a PAT/PMT.
The EXT-X-I-FRAMES-ONLY tag appeared in version 4 of the protocol.
3.4.13. EXT-X-MAP
The EXT-X-MAP tag specifies how to obtain the Transport Stream PAT/
PMT for the applicable media segment. It applies to every media
segment that appears after it in the Playlist until the next EXT-X-
DISCONTINUITY tag, or until the end of the playlist.
The EXT-X-MAP tag MUST NOT appear unless the Playlist also contains
the EXT-X-I-FRAMES-ONLY tag. It is RECOMMENDED that the EXT-X-MAP
tag only be used for segments whose resource does not start with a
PAT/PMT.
Its format is:
#EXT-X-MAP:<attribute-list>
The following attributes are defined:
URI
The value is a quoted-string containing a URI that identifies a
resource that contains the Transport Stream PAT/PMT. This attribute
is mandatory.
BYTERANGE
The value is a quoted-string specifying a byte range into the
resource identified by the URI attribute. This range SHOULD contain
only the Transport Stream PAT/PMT. The format of the byte range is
described in Section 3.4.1. This attribute is optional; if it is not
present, the byte range is the entire resource indicated by the URI.
The EXT-X-MAP tag appeared in version 5 of the protocol.
3.4.14. EXT-X-I-FRAME-STREAM-INF
The EXT-X-I-FRAME-STREAM-INF tag identifies a Playlist file
containing the I-frames of a multimedia presentation. It stands
alone, in that it does not apply to a particular URI in the Playlist.
Its format is:
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#EXT-X-I-FRAME-STREAM-INF:<attribute-list>
All attributes defined for the EXT-X-STREAM-INF tag (Section 3.4.10)
are also defined for the EXT-X-I-FRAME-STREAM-INF tag, except for the
AUDIO and SUBTITLES attributes. In addition, the following attribute
is defined:
URI
The value is a quoted-string containing a URI that identifies the
I-frame Playlist file.
Every EXT-X-I-FRAME-STREAM-INF tag MUST include a BANDWIDTH attribute
and a URI attribute.
The provisions in Section 3.4.10.1 also apply to EXT-X-I-FRAME-
STREAM-INF tags with a VIDEO attribute.
A Playlist that specifies alternative VIDEO renditions and I-frame
Playlists SHOULD include an alternative I-frame VIDEO rendition for
each regular VIDEO rendition, with the same NAME and LANGUAGE
attributes.
The EXT-X-I-FRAME-STREAM-INF tag appeared in version 4 of the
protocol. Clients that do not implement protocol version 4 or higher
MUST ignore it.
3.4.15. EXT-X-VERSION
The EXT-X-VERSION tag indicates the compatibility version of the
Playlist file. The Playlist file, its associated media, and its
server MUST comply with all provisions of the most-recent version of
this document describing the protocol version indicated by the tag
value.
The EXT-X-VERSION tag applies to the entire Playlist file. Its
format is:
#EXT-X-VERSION:<n>
where n is an integer indicating the protocol version.
A Playlist file MUST NOT contain more than one EXT-X-VERSION tag. A
Playlist file that does not contain an EXT-X-VERSION tag MUST comply
with version 1 of this protocol.
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Each media URI in a Playlist file specifies a media segment which is
part of the overall presentation. If a media URI has an EXT-X-
BYTERANGE tag applied to it, the segment is a sub-range of the media
file identified by the URI. Otherwise, the segment is the entire
media file.
Each media segment MUST be formatted as an MPEG-2 Transport Stream
[ISO_13818], an MPEG audio elementary stream [ISO_11172], or a WebVTT
[WebVTT] file.
Transport Stream segments MUST contain a single MPEG-2 Program.
There SHOULD be a Program Association Table (PAT) and a Program Map
Table (PMT) at the start of each segment. A segment that contains
video SHOULD have at least one key frame and enough information to
completely initialize a video decoder.
A Transport Stream or audio elementary stream segment MUST be the
continuation of the encoded media at the end of the segment with the
previous sequence number, where values in a continuous series, such
as timestamps and Continuity Counters, continue uninterrupted -
unless the media segment was the first ever to appear in the Playlist
file or has an EXT-X-DISCONTINUITY tag applied to it.
Clients SHOULD be prepared to handle multiple tracks of a particular
type (e.g. audio or video). A client with no other preference SHOULD
choose the track with the lowest numerical PID that it can play.
Clients MUST ignore private streams inside Transport Streams that
they do not recognize.
The encoding parameters for samples in a stream inside a media
segment and between corresponding streams across multiple media
segments SHOULD remain consistent. However clients SHOULD deal with
encoding changes as they are encountered, for example by scaling
video content to accommodate a resolution change.
Subtitle segments MUST be formatted as WebVTT [WebVTT] files. Each
subtitle segment MUST contain all subtitle cues that are intended to
be displayed during the period indicated by the segment EXTINF
duration. The start time offset and end time offset of each cue MUST
indicate the total display time for that cue, even if that time range
extends beyond the EXTINF duration. A WebVTT segment MAY contain no
cues; this indicates that no subtitles are to be displayed during
that period.
Each WebVTT segment MUST have an X-TIMESTAMP-MAP metadata header.
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This header synchronizes the cue timestamps in the WebVTT file with
the MPEG-2 (PES) timestamps in other streams. Its format is:
X-TIMESTAMP-MAP=LOCAL:<cue time>,MPEGTS:<MPEG-2 time>
e.g. X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
The cue timestamp in the LOCAL attribute MAY fall outside the range
of time covered by the segment.
5. Key files5.1. Introduction
An EXT-X-KEY tag with a URI attribute identifies a Key file. A Key
file contains the cipher key that MUST be used to decrypt subsequent
media segments in the Playlist.
[AES_128] encryption uses 16-octet keys. If the KEYFORMAT of an EXT-
X-KEY tag is "identity", the Key file is a single packed array of 16
octets in binary format.
5.2. IV for [AES_128]
[AES_128] requires the same 16-octet Initialization Vector (IV) to be
supplied when encrypting and decrypting. Varying this IV increases
the strength of the cipher.
If an EXT-X-KEY tag has a KEYFORMAT of "identity" and an IV attribute
is present, implementations MUST use the attribute value as the IV
when encrypting or decrypting with that key. The value MUST be
interpreted as a 128-bit number.
If an EXT-X-KEY tag with a KEYFORMAT of "identity" does not have the
IV attribute, implementations MUST use the sequence number of the
media segment as the IV when encrypting or decrypting that media
segment. The big-endian binary representation of the sequence number
SHALL be placed in a 16-octet buffer and padded (on the left) with
zeros.
6. Client/Server Actions6.1. Introduction
This section describes how the server generates the Playlist and
media segments and how the client should download and play them.
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The production of the media stream is outside the scope of this
document, which simply presumes a source of a continuous stream
containing the presentation.
The server MUST divide the stream into individual media segments
whose duration is less than or equal to a constant target duration.
The server SHOULD attempt to divide the stream at points that support
effective decode of individual media segments, e.g. on packet and key
frame boundaries.
The server MUST create a URI for every media segment that enables its
clients to obtain the segment data. If a server supports partial
loading of resources (e.g. via HTTP Range requests), it MAY specify
segments as sub-ranges of larger resources using the EXT-X-BYTERANGE
tag.
If WebVTT segments are distributed by HTTP, the server SHOULD support
client requests to use the "gzip" Content-Encoding.
The server MUST create a Playlist file. The Playlist file MUST
conform to the format described in Section 3. A URI for each media
segment that the server wishes to make available MUST appear in the
Playlist in the order in which it is to be played. The entire media
segment MUST be available to clients if its URI is in the Playlist
file.
The Playlist file MUST contain an EXT-X-TARGETDURATION tag. Its
value MUST be equal to or greater than the EXTINF value of any media
segment that appears or will appear in the Playlist file. Its value
MUST NOT change. A typical target duration is 10 seconds.
The Playlist file SHOULD contain one EXT-X-VERSION tag which
indicates the compatibility version of the stream. Its value MUST be
the lowest protocol version with which the server, Playlist file, and
associated media segments all comply. Its value MUST NOT change.
The server MUST create a URI for the Playlist file that will allow
its clients to obtain the file.
If the Playlist file is distributed by HTTP, the server SHOULD
support client requests to use "gzip" Content-Encoding.
Changes to the Playlist file MUST be made atomically from the point
of view of the clients.
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The server MUST NOT change the Playlist file, except to:
Append lines to it (Section 6.2.1).
Remove media segment URIs from the Playlist in the order that they
appear, along with any tags that apply only to those segments
(Section 6.2.2).
Increment the value of the EXT-X-MEDIA-SEQUENCE tag
(Section 6.2.2).
Add or remove EXT-X-STREAM-INF tags or EXT-X-I-FRAME-STREAM-INF
tags (Section 6.2.4). Note that clients are not required to
reload variant Playlist files, so changing them may not have
immediate effect.
Add an EXT-X-ENDLIST tag to the Playlist (Section 6.2.1).
Furthermore, the Playlist file MAY contain an EXT-X-PLAYLIST-TYPE tag
with a value of either EVENT or VOD. If the tag is present and has a
value of EVENT, the server MUST NOT change or delete any part of the
Playlist file (although it MAY append lines to it). If the tag is
present and has a value of VOD, the Playlist file MUST NOT change.
Every media segment in a Playlist MUST have an EXTINF tag applied to
it indicating the duration of the media segment.
The server MAY associate an absolute date and time with a media
segment by applying an EXT-X-PROGRAM-DATE-TIME tag to the segment.
The date and time value provides an informative mapping of the
timeline of the media to an appropriate wall-clock time, which may be
used as a basis for seeking, for display, or for other purposes. If
a server provides this mapping, it SHOULD apply an EXT-X-PROGRAM-
DATE-TIME tag to every segment that has an EXT-X-DISCONTINUITY tag
applied to it.
If the Playlist contains the final media segment of the presentation
then the Playlist file MUST contain the EXT-X-ENDLIST tag.
If the Playlist does not contain the EXT-X-ENDLIST tag, the server
MUST make a new version of the Playlist file available that contains
at least one new media segment. It MUST be made available relative
to the time that the previous version of the Playlist file was made
available: no earlier than one-half the target duration after that
time, and no later than 1.5 times the target duration after that
time.
If the server wishes to remove an entire presentation, it MUST make
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the Playlist file unavailable to clients. It SHOULD ensure that all
media segments in the Playlist file remain available to clients for
at least the duration of the Playlist file at the time of removal.
6.2.2. Sliding Window Playlists
The server MAY limit the availability of media segments by removing
media segments from the Playlist file (Section 6.2.1). If media
segments are to be removed, the Playlist file MUST contain exactly
one EXT-X-MEDIA-SEQUENCE tag. Its value MUST be incremented by 1 for
every media segment that is removed from the Playlist file.
Media segments MUST be removed from the Playlist file in the order
that they appear in the Playlist.
The server MUST NOT remove a media segment from the Playlist file if
the duration of the Playlist file minus the duration of the segment
is less than three times the target duration.
When the server removes a media segment from the Playlist, the
corresponding media URI SHOULD remain available to clients for a
period of time equal to the duration of the segment plus the duration
of the longest Playlist file distributed by the server containing
that segment.
If a server plans to remove a media segment after it is delivered to
clients over HTTP, it SHOULD ensure that the HTTP response contains
an Expires header that reflects the planned time-to-live.
6.2.3. Encrypting media segments
If media segments are to be encrypted the server MUST define a URI
which will allow authorized clients to obtain a Key file containing a
decryption key. The Key file MUST conform to the format described in
Section 5.
The server MAY set the HTTP Expires header in the key response to
indicate that the key may be cached.
The server MUST encrypt every media segment in a Playlist according
to the EXT-X-KEY tag that applies to its URI in the Playlist file.
Media segments with an EXT-X-KEY tag whose METHOD is NONE, or which
do not have an EXT-X-KEY tag applied to them, MUST NOT be encrypted.
If the encryption METHOD is AES-128 and the Playlist does not contain
the EXT-X-I-FRAMES-ONLY tag, AES-128 CBC encryption with PKCS7
padding [RFC5652] SHALL be applied to individual media segments. The
entire segment MUST be encrypted. Cipher Block Chaining MUST NOT be
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applied across media segments. The IV used for encryption MUST be
either the sequence number of the media segment or the value of the
IV attribute of the EXT-X-KEY tag, as described in Section 5.2.
If the encryption METHOD is AES-128 and the Playlist contains an EXT-
X-I-FRAMES-ONLY tag, AES-128 CBC encryption with PKCS7 padding
[RFC5652] MUST be applied to the entire resource. The entire
resource MUST be encrypted. Encryption MAY be restarted on 16-byte
block boundaries, unless the first block contains an I-frame. The IV
used for encryption MUST be either the sequence number of the media
segment or the value of the IV attribute of the EXT-X-KEY tag, as
described in Section 5.2.
If the encryption METHOD is SAMPLE-AES, certain elementary streams
MAY be encrypted prior to encapsulation in a media segment. The
encryption format for H.264, AAC and AC-3 elementary streams is
described by [SampleEnc].
The server MUST NOT remove an EXT-X-KEY tag from the Playlist file if
it applies to any media segment in the Playlist file.
6.2.4. Providing variant streams
A server MAY offer multiple Playlist files to provide different
encodings of the same presentation. If it does so it SHOULD provide
a variant Playlist file that lists each variant stream to allow
clients to switch between encodings dynamically.
Variant Playlists MUST contain an EXT-X-STREAM-INF tag or EXT-X-I-
FRAME-STREAM-INF tag for each variant stream. Each tag identifying
an encoding of the same presentation MUST have the same PROGRAM-ID
attribute value. The PROGRAM-ID value for each presentation MUST be
unique within the variant Playlist.
If an EXT-X-STREAM-INF tag or EXT-X-I-FRAME-STREAM-INF tag contains
the CODECS attribute, the attribute value MUST include every format
defined by [RFC6381] that is present in any media segment that
appears or will appear in the Playlist file.
The server MUST meet the following constraints when producing variant
streams:
Each variant stream MUST present the same content, including
stream discontinuities.
Each variant Playlist file MUST have the same target duration.
The only exception is that SUBTITLES renditions with a EXT-X-
PLAYLIST-TYPE of VOD MAY have longer target durations.
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Content that appears in one variant Playlist file but not in
another MUST appear either at the beginning or at the end of the
Playlist file and MUST NOT be longer than the target duration.
Matching content in variant streams MUST have matching timestamps.
This allows clients to synchronize the streams.
Each Elementary Audio Stream segment MUST signal the timestamp of
its first sample with an ID3 PRIV tag [ID3] at the beginning of
the segment. The ID3 PRIV owner identifier MUST be
"com.apple.streaming.transportStreamTimestamp". The ID3 payload
MUST be a 33-bit MPEG-2 Program Elementary Stream timestamp
expressed as a big-endian eight-octet number, with the upper 31
bits set to zero.
In addition, all variant streams SHOULD contain the same encoded
audio bitstream. This allows clients to switch between streams
without audible glitching.
The rules for variant streams also apply to alternate renditions -
see Section 3.4.10.1.
6.3. Client Process6.3.1. Introduction
How the client obtains the URI to the Playlist file is outside the
scope of this document; it is presumed to have done so.
The client MUST obtain the Playlist file from the URI. If the
Playlist file so obtained is a variant Playlist, the client MUST
obtain the Playlist file from the variant Playlist.
This document does not specify the treatment of variant streams by
clients.
6.3.2. Loading the Playlist file
Every time a Playlist file is loaded or reloaded from the Playlist
URI:
The client MUST ensure that the Playlist file begins with the
EXTM3U tag and that the EXT-X-VERSION tag, if present, specifies a
protocol version supported by the client; if not, the client MUST
NOT attempt to use the Playlist.
The client SHOULD ignore any tags and attributes it does not
recognize.
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The client MUST determine the next media segment to load, as
described in Section 6.3.5.
If the Playlist contains the EXT-X-MEDIA-SEQUENCE tag, the client
SHOULD assume that each media segment in it will become unavailable
at the time that the Playlist file was loaded plus the duration of
the Playlist file.
6.3.3. Playing the Playlist file
The client SHALL choose which media segment to play first from the
Playlist when playback starts. If the EXT-X-ENDLIST tag is not
present and the client intends to play the media regularly (i.e. in
playlist order at the nominal playback rate), the client SHOULD NOT
choose a segment which starts less than three target durations from
the end of the Playlist file. Doing so can trigger playback stalls.
To achieve regular playback, media segments MUST be played in the
order that they appear in the Playlist file. The client MAY present
the available media in any way it wishes, including regular playback,
random access, and trick modes.
The client MUST be prepared to reset its parser(s) and decoder(s)
before playing a media segment that has an EXT-X-DISCONTINUITY tag
applied to it.
The client SHOULD attempt to load media segments in advance of when
they will be required for uninterrupted playback to compensate for
temporary variations in latency and throughput.
If the Playlist file contains the EXT-X-ALLOW-CACHE tag and its value
is NO, the client MUST NOT cache downloaded media segments after they
have been played. Otherwise the client MAY cache downloaded media
segments indefinitely for later replay.
The client MAY use the value of the EXT-X-PROGRAM-DATE-TIME tag to
display the program origination time to the user. If the value
includes time zone information the client SHALL take it into account,
but if it does not the client MUST NOT infer an originating time
zone.
The client MUST NOT depend upon the correctness or the consistency of
the value of the EXT-X-PROGRAM-DATE-TIME tag.
6.3.4. Reloading the Playlist file
The client MUST periodically reload the Playlist file unless it
contains the EXT-X-ENDLIST tag.
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However the client MUST NOT attempt to reload the Playlist file more
frequently than specified by this section.
When a client loads a Playlist file for the first time or reloads a
Playlist file and finds that it has changed since the last time it
was loaded, the client MUST wait for a period of time before
attempting to reload the Playlist file again. This period is called
the initial minimum reload delay. It is measured from the time that
the client began loading the Playlist file.
The initial minimum reload delay is the duration of the last media
segment in the Playlist. Media segment duration is specified by the
EXTINF tag.
If the client reloads a Playlist file and finds that it has not
changed then it MUST wait for a period of one-half the target
duration before retrying.
In order to reduce server load, the client SHOULD NOT reload the
Playlist files of variant streams that are not currently being
played. If it decides to switch playback to a different variant, it
SHOULD stop reloading the Playlist of the old variant and begin
loading the Playlist of the new variant. It can use the EXTINF
durations and the constraints in Section 6.2.4 to determine the
approximate location of corresponding media. Once media from the new
variant has been loaded, the timestamps in the media segments can be
used to synchronize the old and new timelines precisely. A client
MUST NOT assume that segments with the same media sequence number in
different variants or renditions contain matching content.
6.3.5. Determining the next segment to load
The client MUST examine the Playlist file every time it is loaded or
reloaded to determine the next media segment to load.
The first segment to load MUST be the segment that the client has
chosen to play first, as described in Section 6.3.3.
If the first segment to be played has been loaded and the Playlist
file does not contain the EXT-X-MEDIA-SEQUENCE tag then the client
MUST verify that the current Playlist file contains the URI of the
last loaded media segment at the offset it was originally found at,
halting playback if it does not. The next media segment to load MUST
be the first media segment following the last-loaded segment in the
Playlist.
If the first segment to be played has been loaded and the Playlist
file contains the EXT-X-MEDIA-SEQUENCE tag then the next media
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segment to load SHALL be the one with the lowest sequence number that
is greater than the sequence number of the last media segment loaded.
6.3.6. Decrypting encrypted media segments
If a Playlist file contains an EXT-X-KEY tag that specifies a Key
file URI, the client MUST obtain that key file and use the key inside
it to decrypt all media segments to which that EXT-X-KEY tag applies.
A client MUST NOT attempt to use an EXT-X-KEY tag with an unsupported
or unrecognized KEYFORMAT attribute. A client SHOULD fail playback
if the Playlist contains a media segment to which only EXT-X-KEY tags
with unrecognized or unsupported KEYFORMAT attributes are applied.
If the encryption METHOD is AES-128, AES-128 CBC decryption SHALL be
applied to individual media segments. The entire segment MUST be
decrypted. Cipher Block Chaining MUST NOT be applied across media
segments. The IV used for decryption MUST be either the sequence
number of the media segment or the value of the IV attribute of the
EXT-X-KEY tag, as described in Section 5.2.
If the encryption METHOD is AES-128 and the media segment is part of
an I-frame playlist (Section 3.4.12) special care MUST be taken in
loading and decrypting the segment, because the resource identified
by the URI is encrypted in 16-byte blocks from the start of the
resource (offset 0). The sub-range specified by the EXT-X-BYTERANGE
tag MUST be widened to include the 16-byte blocks in which the
beginning and end of the sub-range fall. Next, it MUST be widened
further to include the previous 16-byte block. That range MUST be
loaded and decrypted with AES-128 CBC using an arbitrary IV. The
decrypted segment will then be in the original (unwidened) sub-range.
If the encryption METHOD is SAMPLE-AES, AES-128 decryption SHALL be
applied to encrypted elementary streams within the media segment.
The encryption format for H.264, AAC and AC-3 elementary streams is
described by [SampleEnc].
An EXT-X-KEY tag with a METHOD of NONE indicates that the media
segments it applies to are not encrypted.
7. Protocol version compatibility
Clients and servers MUST implement protocol version 2 or higher to
use:
o The IV attribute of the EXT-X-KEY tag.
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In this example, the PROGRAM-ID attributes have been left out:
#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=1280000
low/audio-video.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=86000,URI="low/iframe.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=2560000
mid/audio-video.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=150000,URI="mid/iframe.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=7680000
hi/audio-video.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=550000,URI="hi/iframe.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5"
audio-only.m3u8
8.7. Variant Playlist with Alternative audio
In this example, the PROGRAM-ID attributes have been left out. The
CODECS attributes have been condensed for space. A '\' is used to
indicate that the tag continues on the following line with whitespace
removed:
#EXTM3U
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="English", \
DEFAULT=YES,AUTOSELECT=YES,LANGUAGE="en", \
URI="main/english-audio.m3u8"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="Deutsche", \
DEFAULT=NO,AUTOSELECT=YES,LANGUAGE="de", \
URI="main/german-audio.m3u8"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="Commentary", \
DEFAULT=NO,AUTOSELECT=NO,URI="commentary/audio-only.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=1280000,CODECS="...",AUDIO="aac"
low/video-only.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2560000,CODECS="...",AUDIO="aac"
mid/video-only.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=7680000,CODECS="...",AUDIO="aac"
hi/video-only.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5",AUDIO="aac"
main/english-audio.m3u8
8.8. Variant Playlist with Alternative video
In this example, the PROGRAM-ID attributes have been left out. The
CODECS attributes have been condensed for space. A '\' is used to
indicate that the tag continues on the following line with whitespace
removed:
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Subtype name: "vnd.apple.mpegurl"
Required parameters: (none)
Optional parameters: (none)
Encoding considerations: encoded as text. See Section 3 for more
information.
Security considerations: See Section 11.
Compression: this media type does not employ compression.
Interoperability considerations: There are no byte-ordering issues,
since files are 7- or 8-bit text. Applications could encounter
unrecognized tags, which SHOULD be ignored.
Published specification: see Section 3.
Applications that use this media type: Multimedia applications such
as the iPhone media player in iOS 3.0 and later and QuickTime Player
in Mac OS X version 10.6 and later.
Additional information: files begin with the magic number #EXTM3U.
Filenames normally end with .m3u8 or .m3u (see Section 3). No
Macintosh file type codes have been registered.
Person & email address to contact for further information: David
Singer, singer AT apple.com.
Intended usage: LIMITED USE
Restrictions on usage: (none)
Author: Roger Pantos
Change Controller: David Singer
11. Security Considerations
Since the protocol generally uses HTTP to transfer data, most of the
same security considerations apply. See section 15 of RFC 2616
[RFC2616].
Media file parsers are typically subject to "fuzzing" attacks.
Clients SHOULD take care when parsing segments received from a server
that non-compliant segments are rejected.
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Playlist files contain URIs, which clients will use to make network
requests of arbitrary entities. Clients SHOULD range-check responses
to prevent buffer overflows. See also the Security Considerations
section of RFC 3986 [RFC3986].
Clients SHOULD load resources identified by URI lazily to avoid
contributing to denial-of-service attacks.
HTTP requests often include session state ("cookies"), which may
contain private user data. Implementations MUST follow cookie
restriction and expiry rules specified by RFC 6265 [RFC6265]. See
also the Security Considerations section of RFC 6265, and RFC 2964
[RFC2964].
Encryption keys are specified by URI. The delivery of these keys
SHOULD be secured by a mechanism such as HTTP over TLS [RFC5246]
(formerly SSL) in conjunction with a secure realm or a session
cookie.
12. References12.1. Normative References
[AC_3] Advanced Television Systems Committee, "ATSC Standard:
A/52:2010: Digital Audio Compression (AC-3) (E-AC-3)
Standard", November 2010,
<http://www.atsc.org/cms/standards/a_52-2010.pdf>.
[AES_128] U.S. Department of Commerce/National Institute of
Standards and Technology, "Advanced Encryption Standard
(AES), FIPS PUB 197", November 2001, <http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf>.
[H_264] International Telecommunications Union, "Advanced video
coding for generic audiovisual services", January 2012,
<http://www.itu.int/rec/T-REC-H.264>.
[ISO_11172]
International Organization for Standardization, "ISO/IEC
International Standard 11172-1; Coding of moving pictures
and associated audio for digital storage media -- Part 1:
Systems", 1993,
<http://www.iso.org/iso/catalogue_detail?csnumber=19180>.
[ISO_13818]
International Organization for Standardization, "ISO/IEC
International Standard 13818; Generic coding of moving
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